U.S. patent number 6,589,761 [Application Number 09/661,349] was granted by the patent office on 2003-07-08 for method and apparatus for detecting bacteria.
Invention is credited to Howard C. Beach, Marv Freadman.
United States Patent |
6,589,761 |
Freadman , et al. |
July 8, 2003 |
Method and apparatus for detecting bacteria
Abstract
A device and method for detecting bacteria in food substances
and the like utilizing a three layer composite consisting of a
transparent base, an indicator exhibiting color change when exposed
to changes in pH, and a gas permeable cover placeable in proximity
to the substance. The method utilizes the generation of CO.sub.2
gas as a byproduct of bacterial growth which produces carbonic acid
lowering the pH of the substance in the region of the composite
resulting in an observable color change as in indication of the
presence of bacteria.
Inventors: |
Freadman; Marv (Chelsea,
MA), Beach; Howard C. (Milton, MA) |
Family
ID: |
32995180 |
Appl.
No.: |
09/661,349 |
Filed: |
September 14, 2000 |
Current U.S.
Class: |
435/29;
435/283.1; 435/287.1; 435/287.5; 435/32; 435/807 |
Current CPC
Class: |
C12Q
1/04 (20130101); G01N 33/52 (20130101); G01N
33/84 (20130101); Y10S 435/807 (20130101) |
Current International
Class: |
C12Q
1/04 (20060101); G01N 33/52 (20060101); G01N
33/84 (20060101); C12Q 001/02 (); C12Q 001/18 ();
G01N 033/53 () |
Field of
Search: |
;435/34,29,32,287.5,283.1,807,287.1,968 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Leary; Louise N.
Attorney, Agent or Firm: Brandt; John M.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a formal application based on the disclosure of
provisional application Ser. No. 60/140,052 filed Jun. 19, 1999 by
the same inventors.
Claims
What is claimed is:
1. A device for detecting bacterial growth in a selected substance
wherein a byproduct of said growth is carbon dioxide and wherein
said carbon dioxide in the presence of ambient water results in the
production of carbonic acid yielding an increase in hydrogen ion
concentration and a decrease in pH, said device comprising in
combination: a. a CO.sub.2 impermeable transparent support base; b.
a quantity of an indicator having the property of exhibiting a
color change upon exposure to a decrease in pH disposed upon said
base; c. a CO.sub.2 permeable cover disposed over said indicator
and said base; said base, indicator and cover forming a composite
which when said cover is placed in proximity to said substance will
provide an indication of bacterial growth though an observable
color change of said indicator.
2. The device of claim 1 wherein said indicator is combined with a
gel.
3. The device of claim 2 wherein said indicator comprises an acid
base indicator.
4. The device of claim 2 wherein said indicator comprises a mixed
indicator.
5. The device of claim 2 wherein said indicator comprises a
screened indicator.
6. The device of claim 2 wherein said indicator comprises a
universal indicator.
7. The device of claim 2 wherein said indicator comprises a plant
derived indicator.
8. The device of claim 2 wherein said indicator comprises a
fluorescent indicator.
9. The device of claim 2 wherein said indicator comprises a
luminescent indicator.
10. The device of claim 2 wherein said indicator comprises an
irreversible indicator.
11. The device of claim 2 wherein said indicator comprises a
miscellaneous indicator.
12. The device of claim 1 wherein said composite comprises a sheet
food wrap.
13. The device of claim 1 wherein said composite comprises a
portion of a container for liquids.
14. The device of claim 1 wherein said composite comprises a wafer
for placement in the contact with said substance.
15. A method for detecting bacterial growth in a selected substance
wherein a byproduct of said growth is carbon dioxide and wherein
said carbon dioxide in the presence of ambient water results in the
production of carbonic acid yielding an increases in hydrogen ion
concentration and a decrease in pH, said method comprising in
combination: a. providing a CO.sub.2 impermeable transparent
support base; b. providing a quantity of an indicator having the
property of exhibiting a color change upon exposure to a disease in
pH and disposing said indicator upon said base; c. providing a
CO.sub.2 permeable cover and disposing said cover over said
indicator and said base to provide a composite; and d. placing said
composite and said cover in proximity to said substance to provide
an indication of bacterial growth though an observable color change
of said indicator.
16. The method of claim 15 wherein said indicator is combined with
a gel.
17. The method of claim 16 wherein said indicator comprises an acid
base indicator.
18. The method of claim 16 wherein said indicator comprises a mixed
indicator.
19. The method of claim 16 wherein said indicator comprises a
screened indicator.
20. The method of claim 16 wherein said indicator comprises a
universal indicator.
21. The method of claim 16 wherein said indicator comprises a plant
derived indicator.
22. The method of claim 16 wherein said indicator comprises a
fluorescent indicator.
23. The method of claim 16 wherein said indicator comprises a
luminescent indicator.
24. The method of claim 16 wherein said indicator comprises an
irreversible indicator.
25. The method of claim 16 wherein said indicator comprises a
miscellaneous indicator.
26. The method of claim 15 wherein said composite comprises a sheet
food wrap.
27. The method of claim 15 wherein said composite comprises a
portion of a container for liquids.
28. The method of claim 15 wherein said composite comprises a wafer
for placement in contact with said substance.
Description
BACKGROUND OF THE INVENTION
Field of the invention: The invention resides in the field of
bacteria detection and more particularly relates to a method and
apparatus for real time indication of bacterial presence.
Description of the prior art: From the 1950's through the early
1970's, most of the recognized causes of foodborne diseases and
outbreaks were related to handling of foodstuff, for example,
contaminated hands, insufficient cooking and improper storage by
consumers or improper food preparation. In the 1990's, it is more
frequent that single source outbreaks come from unsafe sources of
food. The Center For Disease Control has estimated that each
American has had at least one episode of foodbome disease per year,
whether it is recognized or not. Another estimate projected that,
annually, between 8 and 80 million people experience foodborne
illnesses and some 9,000 die.
Present methods of bacterial detection known to the inventors
include incubation, DNA polymerase chain reaction, toxin detection,
and protein product degradation. In contrast to the above, we have
devised a real time method to detect the presence of the major
bacteria known to be the cause of foodbome disease, common source
outbreaks and bacterial foodstuff spoilage.
The method of detecting bacteria we have devised is also directly
applicable to ensuring the sterility of medical packaging, the
safety of bottled water, biological weapons detection, drug testing
and the safety of surgical suites.
SUMMARY OF THE INVENTION
The detection method of the invention is based on means to detect
the production of CO.sub.2, a gas normally produced during the life
processes of bacteria responsible for foodborne illnesses. The
detection means comprises a package which is placed in close
proximity to foodstuff of concern at the point of sale or consumer
level. The method of detection is the use of a pH indicator which
will respond to the presence of CO.sub.2 gas by a change in color.
An indicator is placed under currently utilized packaging for
products such as meat, fish, chicken, turkey and pork, in the
middle layer of a three layer package for milk, and as a button in
a bottle cap for many juices. The indicator in the packaging will
not affect the integrity of the foodstuff. Our detection method is
applicable to the major known bacteria which taint food and cause
foodborne illnesses. A large number of chemical indicators which
will serve the purpose of the invention are available and will be
disclosed in detail in the description of the preferred embodiment
which follows.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a plan view of the preferred embodiment of the
invention;
FIG. 2 is a cross-sectional view of FIG. 1 along line A--A;
FIG. 3 is a perspective view of the preferred embodiment
incorporated into a food package; and
FIG. 4 is a perspective view of the preferred embodiment
incorporated into an alternative food package.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The detection of foodbome bacteria is pivotal for prevention of
foodborne illnesses. This invention detects bacteria by a device
incorporateable directly into currently used packaging. The basis
of the method is the detection of CO.sub.2, a gas produced during
the life processes of bacteria which cause foodborne illnesses. The
method of detection is a pH indicator such as phenolpthalein or
indole red which will change color in the presence of CO.sub.2 gas
by the following reaction:
In the increasing presence of CO.sub.2, the hydrogen ion
concentration increases. The pH will thereupon decrease which will
be detected by the pH sensitive material or indicator employed in
the method. As pH is a measure of hydrogen ion concentration, the
indicator incorporated into a suitable package changes color which
can easily be seen by the consumer. The change in color is
therefore directly related to CO.sub.2 production by disease
causing bacteria.
The method of detection of the invention is sensitive to small
changes in pH, which in turn insensitive to low concentrations of
bacteria. This is important for the detection of even a very low
level of deleterious bacteria which can cause foodborne illness and
for other applications as well.
This instantaneous detection method is ideally suited for all of
the major bacteria that are connected to foodborne diseases. In
contrast to prior art, the method of the invention does not rely on
culturing techniques that must be tailored to the specific pathogen
which techniques have limited use in the prevention of bacterial
exposure.
The bacterial species our method detects include Salmonella
enteriitidis, Campylobacter jejuni, Escherichia coli, including
0157:H7 and other less common shiga toxin producers, Staphylococcus
aureus, Shigella dysenteriae, and Listeria monocytogenes. The
method may also detect the presence of other foodborne disease
causing organisms such as Vibrio cholerae, Yersinia enterocolitica
and Acromonas sp.
The present day consumer food network is a complex system including
production, processing, distribution, and consumption. This method
is effective in that from whatever level it is wrapped, continuous
monitoring of the packaged foodstuff can take place. Monitoring
will continue in the consumer's household in the store bought
package or in another package such as a sealable bag using
indicator packets for leftovers to detect pathogenic organisms and
spoilage due to bacteria. Monitoring will also continue when
distribution is to restaurants, airport catering services, or other
public distribution site.
Referring next to FIGS. 1 and 2, the indicator or sensor is
incorporated in the packaging 10 which comprises, for example, a
triple layer plastic wrap. The outer plastic layer 12 is not
CO.sub.2 permeable which protects the indicator from ambient levels
of CO.sub.2 and protects the foodstuff as with current wrapping. An
example of a plastic which has been found to work well is
polyethylene terephthalate. The middle layer 14 contains the
indicator in stripes as a solid or semi-solid gel that does not
bleed, thus maintaining the integrity of the foodstuff The inner
plastic layer 16 is in direct contact with the foodstuff and is
permeable to CO.sub.2, through, for example, mechanical
perforations 17 or by the use of a plastic which is in and of
itself permeable to CO.sub.2 such as polyethylene.
The sensor or indicator may be located in a strip across,
crisscrossing or evenly distributed throughout the plastic wrap, as
would be appropriate for packaged chicken, turkey, ground beef,
fish and other solid or semi-solid foodstuff 18 and as is
illustrated in FIG. 3.
The three-layer wrap or package of the invention with the indicator
in the middle layer may be used for any food product.
Alternatively, for packaged meats including sliced variations and
hot dogs, pork, chicken and turkey, a triple layer packet of
defined size is included with the sensor or detector under
conventional packaging. In addition, a similar unit could be
incorporated into a button or wafer and placed in a cap for juices
or bottled water.
As shown in FIG. 4, for liquid containers, for example, for milk or
non-carbonated juice, the three layer composite of the invention
may be located in a strip down the side of and forming an integral
part of container 20.
The method utilizing the above described device for detecting
bacterial growth in a substance wherein a byproduct of the growth
is carbon dioxide which, in the presence of ambient water, results
in the production of carbonic acid yielding an increase in hydrogen
ion concentration and a decrease in pH is as follows:
Provide the above described C02 impermeable transparent support
base and dispose thereon a quantity of an indicator having the
property of exhibiting a color change upon exposure to a decrease
in pH. Thereafter provide the above described CO2 permeable cover
and dispose it over the indicator to provide a composite and
thereafter place the above described composite in proximity to the
subject substance to provide an indication of bacterial growth
through the observable color change of the indicator. In the above
described method, the indicator may be combined with a gel and may
be characterized as of one or more of a variety of indicators to be
further listed below including an acid base, mixed, screened,
universal, plant derived, fluorescent, luminescent, irreversible,
or miscellaneous indicator. Additionally, the composite may consist
of a sheet food wrap, a portion of a container for liquids, and or
a wafer of appropriate size.
A large variety of indicators have been determined to work to
detect CO.sub.2 produced by the bacterial species listed earlier in
the specification. The detection occurs as CO.sub.2 produced by the
bacteria migrates into the indicator mixed in agar or gelatin,
semi-solid or solid, and causes a change in pH of the indicator-gel
environment. The result is a change in the color of the indicator
which is indicative of the presence of bacteria which can cause
foodborne illness. The sensitivity of the indicator-gel (agar or
gelatin based detector) can be adjusted to detect various
concentrations of bacterial species. The concentrations of the
indicators can be varied to take into account potential risks of
contamination. Suitable indicators may also include natural
indicators in the form of compounds derived from plants such as
beets or cabbage. The agar or gelatin base with which the indicator
is combined will not harm the integrity of the foodstuff. Further,
the list of workable indicators includes compounds which differ in
their pH ranges and color changes. It is also contemplated that two
or more indicators may be mixed to provide greater flexibility in
designing suitable packages for various applications.
It has been determined that all indicators listed below work to
detect the presence of bacterial species responsible for foodborne
illness. The indicator-gel combination undergoes a change in pH and
hence, color change, as a result of the production of CO.sub.2 by
bacteria.
For all applications of concern, if bacteria are not present, the
indicator will not change color. It is expected that through
experimentation, modifications and refinements can be carried out
to determine the best indicator-gel detection system based on
bacterial species concentration, indicator concentration,
temperature, and expected illumination of the completed package as
determined by the specific application of the method.
The indicators listed below comprise various groups of indicators.
The groups are regular acid-base indicators, mixed indicators,
screened indicators, universal indicators, pH sticks, litmus paper
(embedded in gel or litmus in a gel), natural food indicators,
fluorescent indicators, luminescent indicators, irreversible
indicators and a miscellaneous group. Many of these indicators can
exist either in a water soluble form or an alcohol based form.
Indicators that have been found to work include but are not limited
to: ACID-BASE INDICATORS: Acid Fuchsin (red-yellow) Alkali Blue 6B
Solution (alcoholic blue-red titrations) Alizarin (yellow-red)
Alizarin Red S (yellow-red) Alizarin Yellow R (yellow-red) Alizarin
Complexone, dihydrate (yellow-red) Andrade indicator with agar
(yellow-red) Anilinesulfonphthalein (colorless-yellow) Aniline
yellow (colorless-yellow) Arsenazo (black/purple-light blue)
Azolitmin (red-blue) Azo violet (red/brown-yellow) Benzopupurine
(violet-red) Bindschedlers green (green-yellow) 2,2'-Bipyridyl
(orange-light yellow) 4,4'-Bis(2-amino-1-napthylazo)
2,2-stilbenedisulfonic acid (purple-red)
4,4'-Bis(4-amino-1-napthylazo) 2,2-stilbenedisulfonic acid
(brown-red) Brilliant Green (yellow-green) Brilliant Orange
(yellow-red) Brilliant Yellow (yellow-red) Bromocresol Green
(yellow-blue) Bromocresol Purple (yellow-purple) Bromochiorophenol
Blue (yellow-blue/violet) Bromophenol Blue (yellow-blue)
Bromophenol Red (yellow-red) Bromopyrogallol Red (yellow-red)
Bromothymol Blue (yellow-blue) Bromoxylenol Blue (yellow-blue)
Calcein/Fluorexon (orange-light yellow) Calconcarboxylic Acid
(orange-yellow) Calmagite (dark brown-light yellow) Carboxyarsenazo
III (dark brown-light blue/yellow) Chlorophenol Red (yellow-red)
Clayton Red (yellow-red) Clayton Yellow (yellow-amber) Cochineral
(orange-yellow) Congo Red (blue-red) o-Cresolphthalein (red-yellow)
Cresol Purple (red-yellow) Cresol Red, 1st and 2nd range
(red-yellow) Crystal Red (yellow-blue) Cresolphthalein (yellow-red)
Crystal Violet (yellow-blue) Curcumin (Tumaric) (yellow-red)
Cyanide Acid Blue (blue-red) Debrisoquine sulfate
3,4-Dihydro-2-[1H]-isoquinoli (yellow-red) p-(2,4
Dihydroxyphenylazo) benzenesulfonic acid, sodium salt
((yellow-orange) p-Dimethylaminoazobenzene (red-yellow)
4-(n,N-Dimethylamino)azobenzene (red-yellow) N
2,n2-dimethylquanosine (red-yellow)
4-(4-Dimethylamino-1-naphylazo)-3-methoxybenzenesulfonic acid
(violet-yellow) 3-(4-Dimethylamino-1-naphylazo)-4-methoxybenzene
(violet-yellow) 2-(p-Dimethylaminophenylazo)pyridine (yellow-blue)
Dimethylsulfonazo III (yellow-blue) Diphenylalanine-4-sulfonic acid
barium salt (yellow-blue) Diphenyl-4-Sulfonic acid sodium salt
(yellow-blue) N,N-Dimethyl-p-(m-tolylazo)anlline (red-yellow)
2,4-Dinitrophenol (colorless-yellow) 2,5-Dinitrophenol
(colorless-yellow) 2,6-Dinitrophenol (colorless-yellow) Diphenol
Purple (yellow-purple) 2-(2,4
Dinitrophenylazo)-1-naphthol-3,6-disulfonic acid, sodium salt
(yellow-red) 6,8-Dinitro-2,4-(1H)quinazolinedione
(colorless-yellow) Diphenylalanine (yellow-blue)
Diphenylalanine-4-sulfonic acid sodium salt (yellow-blue) Eosin
(pink-red/purple) Epsilon Blue (orange-violet) Erichrome Blue Black
R (blue/black-violet) Erythrosin, disodium salt (orange-red)
4-(p-Ethoxyphenalzo)-m-phenylene-diamine monohydrochloride
(orange-yellow) Ethyl bis(2,4-dimethylphenyl) ethanoate
(colorless-blue) Ethyl Orange (red-yellow) Ethyl Red
(colorless-red) Ethyl Violet (yellow-blue) Fast Sulphon Black F
(black-light blue/yellow) Ferroin Solution (red-green) Fluorexon
(yellow-blue) Hematoxylln (brown-yellow)
8-hydroxypyrene-1,3,6-trisulfonic acid (colorless-blue) Indigo
Carmine (blue-yellow) 5,5'-Indigodisulfonic acid, disodium salt
(blue-yellow) Indigo Trisulfonate Potassium Salt (blue-yellow)
Indole Pentasodium (blue-yellow) Indolphenol Sodium Salt
(blue-yellow) Leucocrystal violet (blue-yellow) Litmus (Azolitmin)
(red-yellow) Malachite Green (yellow-blue/green) Metacresol Purple
(red-purple) Metanil Yellow (red-yellow) Methylene Blue (deep
green-blue) Methyl Green (yellow-blue) 4-Methylumbelliferone
methyleneminodiacetic acid (red-orange) Methyl Orange (red orange)
Methyl Purple (red-orange) Methyl Red (red -yellow) Methylthymol
Blue (green/brown-yellow) Methyl Violet (yellow-blue) Methyl
Viologen (yellow-blue) Methyl Yellow (colorless-yellow) Murexide
Powder (deep red-yellow) 1-Naphthobenzein (yellow-green)
o-Naphtholbenzein (yellow-green) p-Naphtholbenzein (yellow-blue)
a-Naphthoflavone (yellow-blue) Naphtholphthalein (yellow-blue)
1-Naphthyl Red (yellow-blue) Neutral Red (red-yellow) Nitramine
(colorless-orange/brown) Nitroaniline (yellow-green) Nitrazine
Yellow Powder (yellow-green) 4-Nitrophenol (colorless-yellow)
3-Nitrophenol (colorless-yellow) p-Nitrophenol (colorless-yellow)
Nitrosulfonazo III (colorless-yellow) Orange G (red-yellow) Orange
1 (Tropaeolin 000 No. 1) (rose-yellow) m-Orange IV (Tropaeolin 00)
(red-yellow) Oregon Green/derivatives like Oregon Green carboxylic
acid (deep green-yellow) Paramethyl Red (red-yellow) Patent Blue
(deep blue-yellow) 1,10-Phenolanthronine (colorless-yellow)
5-Nitro-1,10-phenanthroline hydrate (colorless-pink) Phenolpthalein
(colorless-pink) Phenolphthalin 2-[Bis4-hydroxyphenylmethyl]benzoic
(colorless-pink) Phenol Red (yellow-red) Phenol Red Sodium Salt
(yellow-red) Phenol Violet (yellow-blue) 4-Phenylazodiphenylamine
(red-yellow) 4-Phenylazo-1-naphthylamine (red-yellow) Phloxine B
(red/brown-yellow) Picric acid (yellow-colorless) Poirrier Blue
(blue-red) Propyl Red (red-yellow) 1(2-Pyridylazo)-2-naphthol
(red-yellow) Pyrocatechol Violet (red-yellow) Pyrogallol Red (deep
yellow-colorless) Pyrogallolpthhalein (pale-orange)
Pyrogallosulfonphthalein (yellow-colorless) Quinoline Blue
(colorless-blue) Quinaldine Red (colorless-red) Resazurin
(red-blue) Resorcin Blue (red-blue) Resorcinol (red-blue)
4-(2-Pyridylazo)resorcinol monosodium salt (red-blue)
4-(2-Pyridylazo)resorcinol disodiun salt (red-blue) Resorinol
Yellow (Tropeolin 0) (yellow-orange/brown) Rhodamine
(orange/pink-violet) Rosalic Acid (yellow/brown-red) Rose Bengal
(red-yellow) Safanin (red-yellow) SPADNS (varies) Tartrazine
(colorless-yellow) Tartrazine Yellow (colorless-yellow) Tashiro's
indicator (red/brown-yellow) Tetrabromophenol (yellow-brown)
Tetrabromophenolphthalein (yellow-brown) Tetrabromophenolphthalein
ethyl ester, potassium salt (yellow-brown)
3,4,5,6-Tetrabromophenolsulfonephthalein (yellow-brown)
3,3,5,5-Tetraiodophenolphthalein (yellow-brown)
3,3,5,5-Tetraiodophenolsulfonephthalein (yellow-brown) Thiazole
Yellow G (colorless-yellow) Thorin (red/brown-yellow) Thymol Blue
(yellow-blue) Thymol Blue Sodium Salt (red-yellow) Thymolphthalein
(colorless-blue) Thymol Violet (yellow-green/violet) Titan Yellow
(yellow-red) 4-o-Tolyazo-o-toluidine (orange-yellow)
5,5'7-Trisulfonic acid tripotassium salt (yellow-colorless)
1,3,5-Trinitrobenzene (colorless-orange) 2,4,6-Trinitrobenzene
(colorless-orange) 2,4,6 trinitrotoluene (colorless-orange)
Tropaeolin (yellow-orange/brown) Universal indicator sticks
(varies) Xylene Orange Tetrasodium Salt (red-yellow) Xylenol Blue
(red-yellow) Xylenol Orange (red-yellow) Xylenecyanol FF
(red-yellow) MIXED INDICATORS: methyl yellow and methylene blue (in
alc.) (blue/violet-green) xylene cyanol (in alc). and methyl orange
(in aq.) (violet-green) methyl orange and indigo carmine (in aq.)
(violet-green) methyl orange and aniline blue (in aq.)
(violet-green) bromocresol green sodium and methyl orange (in aq.)
(orange-blue/green) bromocresol green and methyl red (in aq.)
(wine/red-green) methyl red and methylene blue (On alc.)
red/violet-green) chlorophenol red sodium (in aq.) and aniline blue
(in aq.) (green-violet) bromocresol green sodium and chlorophenol
red sodium (in aq.) (green-violet) bromocresol purple sodium and
bromothymol blue sodium (in aq.) (violet-blue) bromothymol blue
sodium and azolitimin (in aq.) (violet-blue) neutral red and
methylene blue (in alc.) (violet-blue/green) neutral red and
bromothymol blue In alc.) (rose-green) cyanine and phenol red (in
alc.) (yellow-violet) bromothymol blue sodium and phenol red sodium
(in aq.) (yellow-violet) cresol red sodium and thymol blue sodium
(in aq.) (yellow-violet) a-naphtholphthalein and cresol red (in
alc.) (pale rose-violet) a-naphtholphthalein and phenolphthalein
(in alc.) (pale rose-violet) phenolphthalein and methyl green (in
alc.) (green-violet) thymol and phenolphthalein (in alc.)
(yellow-violet) phenolphthalein and thymolphthalein (in alc.)
(colorless-violet) phenophthalein and Nile blue (in alc.)
(blue-red) thymolphthalein and alizarin yellow (in alc.)
(yellow-violet) Nile blue (in aq.) and alizarin yellow (in alc.)
(red-brown) SCREENED INDICATORS: Dimethyl yellow and Methylene Blue
(pink-yellow green) Methyl orange and Xylene-cyanol (mauve-green)
Methyl orange and Aniline green (violet-green) Methyl orange and
fluorescein (orange-green) Methyl red and Methylene blue
(mauve-green) Chlorophenol red and Aniline Blue (green-violet)
Neutral red and Methylene blue (blue violet-green) Phenolphthalein
and Methyl green (green-violet) Phenol red and methylene blue
(red-blue) Phenolphthalein and methyl green (colorless-green)
Phenolphthalein and nile blue (colorless-blue) Nile blue and
alizarin yellow (blue-yellow) UNIVERSAL INDICATORS:
There are many examples of universal indicators. They respond over
a wide pH range. Examples are: Yamada's universal indicator (pH
range 4-10, red-orange-yellow-green-blue-deep blue-violet) van
Urk's universal indicator (pH range 2-8,
orange/red-red-yellow-green/yellow-green) NATURAL FOOD OR PLANT
INDICATORS (derived from Red cabbage and purple cabbage): Red
cabbage and purple cabbage (red yellow) Chinese Cabbage Kimchi
(red-yellow) Radishes (red-yellow) Red Onions (red-yellow)
Strawberrys (red yellow) Blackberries (red-yellow) Rasberries
(red-yellow) Cranberries (red-yellow) Grapes (red-yellow) Plums
(red-yellow) Cherries (red-yellow) Beets (red-yellow) Carnation
flowers (varies) Purple Dahlias (purple-yellow) Purple Hollyhocks
(purple -yellow) Red Geraniums (red-yellow) Blue Iris (blue-yellow)
Hydrangeas (varies) Roses (varies) Pomergranates (red-yellow)
Native/non-poisonous plants (varies) FLUORESCENT INDICATORS:
Benzoflavine (yellow-green) 3,6-Dioxyphthalimide (blue-green)
Eosine YS (yellow color-yellow flock) Erythrosine (yellow
color-yellow flock) Esculin (colorless-blue) 4-Ethoxyacridone
(green-blue) 3,6-Tetramethyldiaminooxanthone (green-blue)
Chromotropic acid (colorless-blue) Fluorescein and derivatives like
dichlorofluorescein (colorless-blue) Magdala Red (purple
color-purple flock) a-Naphthylamine (colorless-blue)
b-Naphthylamine (colorless-violet) Phloxine (colorless-bright
yellow) Salicylic acid (colorless-blue) Acridine (green-violet)
Dichlorofluorescein (colorless-green) 3,6-Dioxyanthone
(colorless-blue/violet) Erythrosine (colorless-yellow/green)
b-Methylesculetin (colorless-blue) Neville-Winther acid
(colorless-blue) Resorufin (yellow-weak orange) Quininic acid
(yellow-blue) Quinine (yellow-violet) Acid R Phosphine (yellow-red)
Brilliant Diazol Yellow (colorless-violet) Cleves acid
(colorless-green) Coumaric acid (colorless-green) 3,6-Dioxyphthalic
dinitrile (blue-green) Magnesium 8-hydroxyquinolate
(colorless-golden) b-Methylumbelliferone (colorless-blue)
1-Naphth-4-sulfonic acid (colorless-blue) Orcinaurine
((colorless-green) Patent Phosphine (green-yellow) Thioflavine
(yellow color-yellow flock) Umbelliferone (colorless-blue) Acridine
Orange (orange-green) Ethoxyphenylnaphthostilbazonium chloride
(green color-green flock) G Salt (dull blue-bright blue) Naphthazol
derivatives (colorless-yellow/green) a-Naphthionic acid
(blue-green) 2-Naphthol-3,6-disulfonic acid (dark blue-light blue)
B-Naphthol (colorless-blue flock) a-Naphtholsulfonic acid (dark
blue-bright violet) 1,4-Naphthosulfonic acid (dark blue-light blue)
Orcinsulfonphthalein (yellow color-yellow flock) Quinine
(yellow-black) R-Salt (violet-colorless) Sodium
1-naphthol-2-sulfonate (dark blue-bright violet) Coumarin (deep
green-light green) Eosine BN (colorless-yellow) papaverine
(permanganate oxidized) (yellow-blue) Schaffers Salt
(violet-green/blue) SS-Acid (sodium salt) (violet-yellow) Cotarnine
(yellow color-white flock) a-Naphthionic acid (blue-green)
b-Naphthionic acid (blue flock-green color) LUMINESCENT INDICATORS:
Eosin (colorless-green) Chromotropic acid (colorless-blue)
Fluorescein (colorless-green) Dichiorofluorescein (colorless-green)
Acridine (green violet) b-Naphthol (blue-violet) Quinine
(violet-colorless) IRREVERSIBLE INDICATORS: Amaranth
(red-colorless) Bordeaux (faint pink-yellow/green) Brilliant
Ponceaux (orange-colorless) Napthol Blue Black (green-faint pink)
MISCELLANEOUS INDICATORS: Chemiluminescent indicators such as
luminol, lucigenin and lophine (varies) SNARF pH indicators
(varies) NERF pH indicators (varies) Dextran indicators (ex.
fluoescein tetramethylthrodamine dextran) (varies) Lipophilic
indicators (varies) Reactive indicators (varies) Lysosensor
indicators (varies) Rhodol derivatives (varies) Radical Scavenger
indicators (varies) Coffee extracts (varies) Tea extracts (varies)
Herb extracts (varies)
The color combinations after each indicator show the color change
the indicator undergoes with a change in pH from exposure to
CO.sub.2 produced by bacterial growth. The first color is the base
color and the second, the exposed or changed color.
Some of the mixed indicators provide very distinct color changes
associated with pH changes. These would be advantageous for use at
the consumer level.
Natural indicators can be derived from a variety of foods and
plants. The class of compounds called anthocyanines change color
over different pH ranges and would therefore change color as a
result of CO.sub.2 production by bacteria. The above list includes
examples of foods from which a pH indicator can be prepared. Also
included are flower pedals, fruits, and fruit juices. The great
advantage of natural indicators is that they are less likely to be
associated with risks for most consumers.
Fluorescent indicators can display greater sensitivity and these
may be extremely useful at the production level. This category of
indicators show definite changes in fluorescense with change in pH
as caused by CO.sub.2 production by bacteria. Luminescent and
chemiluminescent indicators show detectable changes in pH
measurable by ultraviolet light and may also be especially useful
at the production level.
The utilization of irreversible indicators in our innovation may
offer the safest and most definitive method to detect the presence
of bacteria in food. This could be relevant if the packaging is
CO.sub.2 permeable and CO.sub.2 migrates outward. An irreversible
indicator, once its color is changed by a change in pH, will not
revert to its original color.
Radical scavenger indicators are detectable by UV or visible
absorption or fluorescense equipment and may be more suitable for
the detection of bacteria at the production level.
The invention disclosed herein is not only applicable to the
detection of bacteria to prevent foodborne illness from consumable
solids and liquids, but may also be used for other related purposes
such as insuring sterile medical packaging, the safety of surgical
suites, biological weapons detection and drug testing. The
invention is accordingly defined by the following claims.
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